Create Folder - Insufficient user rights error

I'm testing API capabilities with a permanent access token. What I'm developing will not be publicly available, so I don't really need to jump through the OAuth2 hoops, but...

I can do all the GET commands I've tested. But when I tried my first POST, creating a project, I got an error back saying:

{"errorDescription":"Operation is not allowed due insufficient user rights or account license limitations","error":"not_allowed"}

Here's the query string I sent:

title=Testing API Creation&description=Testing the Wrike API by creating this folder.&project={"status":"OnHold","startDate":"2022-05-19","endDate":"2022-06-19","contractType":"Billable","budget":100}

I read on another thread that this sort of thing could be caused by using the permanent access token. Which begs the question: What good is a permanent access token? It's only useful for GET commands?

The only other thing I could think may be happening is that I'm still on a trial. Does that limit API capability?

Seemed like @... knew a lot about this, so I figured I'd ask here.

I have submitted this question to support as well. I will post the solution, if there is one, once we figure out what's going on. :-)

Thanks!